1. Field
The present disclosure relates generally to composite structures and, in particular, to layups for composite structures. More particularly, the present disclosure relates to a method and apparatus for determining a layup for a composite structure.
2. Background
Aircraft are being designed and manufactured with greater and greater percentages of composite materials. Composite materials are used in aircraft to decrease the weight of the aircraft. This decreased weight improves performance features such as payload capacity and fuel efficiency. Further, composite materials provide longer service life for various components in an aircraft.
Composite materials may be tough, light-weight materials created by combining two or more functional components. For example, a composite material may include reinforcing fibers bound in a polymer resin matrix. Resins used in composite materials may include thermoplastic or thermoset resins. A thermoplastic material may become soft upon heating and may harden upon cooling. A thermoplastic material may be able to be repeatedly heated and cooled. A thermoset material may become hard when heated. The fibers may be unidirectional or may take the form of a woven cloth or fabric.
In manufacturing composite structures, layers of composite material are typically laid up on a tool. The layers may be comprised of fibers in sheets. These sheets may take the form of fabrics, tape, tows, or other suitable forms. In some cases, resin may be infused or preimpregnated into the sheets. These types of sheets are commonly referred to as prepreg.
The different layers of prepreg may be laid up in different orientations, and different numbers of layers may be used depending on the thickness of the composite structure being manufactured. These layers may be laid up by hand or by using automated equipment such as a fiber placement system. After the layers of composite material have been laid up on the tool, the layers of composite material may be consolidated or cured by exposure to temperature and pressure, thus forming the final composite structure.
Traditional composite structures may include four types of composite layers: 0 degree layers, 45 degree layers, −45 degree layers, and 90 degree layers. These four angles may be conventionally and widely used to form composite structures such as composite skins. The behavior of a composite structure may be changed by varying the number of the four kinds of composite layers.
Advances in manufacturing equipment may now enable use of other fiber angles in composite layers. However, methods of designing composite structures with non-traditional angles of composite layers are needed. Further, methods of analysis for expected performance of composite structures with non-traditional angles of composite layers are needed. Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues.